One type of bioreactor to be found frequently is the stirred tank with a rigid container, which mostly is formed of stainless steel, more rarely of glass or glass-fiber-reinforced plastics. A stirrer with one or more stirring elements arranged in the container ensures intermixing of the liquid present in the container. When adding substances to the liquid present in the container, such as a correcting agent, a fast and uniform distribution is desirable. The same applies in the case of gassing of the liquid; the introduced gas bubbles also should be kept in the liquid as long as possible.
To prevent the formation of clots which occur during stirring when the liquid present in the container rotates with the container, and to produce an increased turbulence, obstacles in the form of flow spoilers, so-called baffles, can be mounted on the container wall. These components protruding into the container “disturb” the uniform course of the flow of the liquid in the container and thereby can considerably improve intermixing. With regard to the cultivation of microorganisms in bioreactors, the baffles provide for distinctly higher stirring speeds. This in turn allows an increased input of oxygen into the liquid, which is indispensable for this kind of cultivation.
An example for a stirred tank with baffles radially protruding from the rigid container wall can be found in U.S. Pat. No. 7,547,135 B2.
To avoid the sterilization effort before on-site use of a bioreactor, pre-sterilized disposable containers with flexible walls are used to an increased extent. These bag-like containers can be folded together for transport in a space-saving way and before use generally are inserted into a support container, although other supporting structures for holding the disposable containers partly filled with very large amounts of liquid also are known. Pre-sterilized disposable containers already can be equipped with a plurality of pre-mounted hoses. In addition, pre-sterilized stirring elements can be integrated into the bags, which e.g. via magnetic bodies in the interior of the bag are coupled with an external stirrer motor of the bioreactor.
From WO 2005/118771 A2 and WO 2007/124847 A1 container assemblies as mentioned above are known. To improve the mixing operation, there are also provided baffles which are mounted on the inner wall of the support container. The lateral wall of the flexible disposable container clings to the inner wall of the support container with the integrally molded baffles, so that the baffles—covered by the wall of the disposable container—can fulfill their function.
This solution has the advantage that the disposable container can be of simple design, as it need not be provided with baffles itself, and that the baffles of the support containers can be used again and again. The number, arrangement and shape of the baffles at the support container however are fixed and cannot be varied. It must also be noted that the wall of the disposable container is greatly deformed at the baffles and therefore is exposed to a great load. Another disadvantage of this construction consists in that the baffles reduce the effective bearing surface of the disposable container wall on the inner wall of the support container, which renders a dissipation of heat from the disposable container to the support container more difficult.
A similar construction of a container assembly like in the above-mentioned documents WO 2005/118771 A2 and WO 2007/124847 A1 also is shown in WO 2009/074213 A1. Here, the baffles at the support container additionally can be equipped with a tempering system, in order to promote uniform and fast tempering. For this purpose, the baffles include parallel tubes through which a liquid can be passed with a specified temperature.
Another alternative to the provision of baffles when using a disposable container would be shrink-wrapping of a rigid plastic part into the flexible bag. However, due to the transport of the disposable container in the compressed condition this is not possible or at least not possible without loss of space and additional safety measures.
U.S. Pat. No. 8,500,322 B2 proposes a mixing device with a plastic bag which is inserted into a rigid support container and includes a baffle in the form of a perforated film web. The film web extends between at least two inner surfaces of the bag, such as from the upper to the lower surface or between two lateral surfaces. The film web hence always traverses the entire bag. The perforation only partly allows the liquid put into motion by the stirrer to flow through the film web.
From WO 2014/172047 A1 there is furthermore known a disposable bioreactor with a flexible baffle, which includes two intersecting legs. The ends of the baffle all are attached to the inner wall of the bioreactor.
JP 2014-121302A shows a cell culture container with a stirrer and a baffle made of plastics, which in the container extends in direction of the stirrer axis. The baffle is inserted between two opposed vertically extending edges of two film portions from which the main container portion is formed. The fixation of the baffle at the film edges is effected by welding (heat sealing). The stability of this fixation however is limited. The baffles are provided with holes through which the substance to be cultivated can pass. Due to the shear forces produced thereby, the holes can turn out to be unfavorable for biological material. The use of perforated baffles preferably should be seen in media with microcarrier cell cultures.